1. Field of the Invention
The present invention relates to a roll arrangement of a machine for producing paper and/or cardboard wherein a roll includes a hollow space arrangement and a heating device that acts on the roll from the exterior. The present invention further relates to a method for cooling a roll.
2. Discussion of Background Information
A roll arrangement that includes a hollow space arrangement and a heating device that acts on the outside of the roll is described in DE 44 10 675 A1.
Generally, roll arrangements that include a roll with a hollow space arrangement and a heating device acting on the exterior of the roll are used with other rolls to impart heat and pressure on a web, particularly a fibrous pulp web, to improve certain characteristics of the pulp. For example, where a paper pulp web is concerned, producing gloss and/or smoothness may be important or it may be important to compress the paper web.
The heating device creates higher temperatures on the surface of the roll, which then may act on the web. However, the heat that is supplied to the surface of the roll may also penetrate other areas of the roll, which then function like heat accumulators so to speak. After turning off the heating device, there is always a certain period of time one must wait before the roll is cool enough to be handled. It may, however, be necessary to handle the roll when, or example, the roll needs to be changed.
It is known to cool the rolls by equipping the rolls with attachments that include cooling water to flush the roll. The flushing removes the heat relatively quickly, but the cooling water causes a considerable increase in the weight of the roll so that the bearing must have greater dimensions. Further, one particular disadvantage with this system is the relatively great thermal stresses that are caused by the difference in temperature between the roll and the cooling water that flushes it. The varying heat stresses occur in an axial direction. The water flowing into the roll on one side has a lower temperature which increases as the water flows over the roll. The cost to control this thermal stress is relatively high.